My 94 855T did the same thing. Ultimately traced to a faulty camshaft position sensor that is easy to replace. 850's are also known to experience "lawnmower syndrome" this condition results from the car being started to "get the mower out from the garage" and then stopped with a re-start attempt shortly thereafter. More common in winter and doesn't sound like it applies here. Incidentally, no codes were set when my camshaft position sensor died. Symptoms were that it would randomly not start but often if one waited a bit 5 - 20 minutes it would start. I have two 94 855T's which makes it easy to swap parts and see if that fixes the problem.

Good luck